Bay platforms would likely be tracks 5 through 8. Those are the longest tracks/platforms in the station, and can each hold a pair of full-length GO trains.
Dan
Toronto, Ont.
True. I just figured you would want the central 'split' (the platform area between the EB and WB tracks) to be at the north end of the station, accessible directly from the Great Hall (without having to go down to any of the concourses and then back up), as opposed to in the dead middle of the station, where it would only be accessible from the concourses below.
Also, if length is an issue, they can be extended slightly beyond the trainshed.